1. Field of the Invention
The present invention relates to a contact-type image sensor used for an image input section of a facsimile machine and so on.
2. Discussion of Background
FIG. 6 is a cross-sectional view of a conventional image sensor disclosed in Japanese Unexamined Patent Publication JP-A-6-18814. In FIG. 6, numerical reference 10a designates a manuscript guiding path; numerical reference 20 designates a linear light source, in which LED chips are linearly arranged; numerical reference 30 designates an erect 1xc3x97 magnification-image-forming rod lens array including a plurality of rod lenses (not shown); numerical reference 40 designates a sensor board; numerical reference 50 designates a sensor ICs, which are linearly arranged on the sensor board 40; numerical reference 60a designates a transparent plate positioned on a manuscript guiding surface; numerical reference 70 designates a frame; and numerical reference 70a designates a protrusion being a part of the frame 70 and fixing the transparent plate 60a to the frame. Numerical reference 80 designates a path of a light emitted from the linear light source 20, which light forms an image in the sensor ICs 50; and numerical reference 90 designates a roller conveying a manuscript.
In the next, an operation will be described. A light from the linear light source 20 passes thought the transparent plate 60a and illuminates the manuscript. The illuminating light is reflected by the manuscript along the light path 80 in response to light-and-shade information of an image. The reflected light passes through the rod lens of the rod lens array 30 and forms an image in the sensor ICs 50. The sensor ICs 50 accumulate electric charges in response to the intensity of the reflected light and outputs image data through the sensor board 40.
As illustrated in FIG. 6, the height of the surface on a side of guiding the manuscript of the transparent plate 60a and the height of the protrusion 70a of the frame are different.
FIG. 7 is a cross-sectional view of a conventional image sensor illustrated in Japanese Unexamined Utility Model Publication JP-A-4-86366. The same numerical references are used for constitutional elements same as those in FIG. 6. Numerical reference 10b designates a manuscript conveying path. A protrusion 70b fixes the transparent plate 60a in a manner similar to that illustrated in FIG. 6. A surface of the transparent plate 60a on a side of guiding the manuscript and the height of the protrusion 70b of the frame are different.
FIG. 8 is a cross-sectional view of a conventional image sensor disclosed in Japanese Unexamined Patent Publication JP-A-5-83469. The same numerical references are used for constitutional elements same as those of the image sensor illustrated in FIG. 6. Numerical reference 10c designates a manuscript conveying path. A transparent plate 60b has a chamfer, and an angle of a protrusion 70c of the frame is determined in correspondence with an angle of the chamfer.
In FIG. 8, the height of the frame 70 is same as the height of a surface of the transparent plate 60b on a side of guiding the manuscript. However, because of a dimensional tolerance of contact surfaces between the frame 70 and the transparent plate 60b, the transparent plate 60b warps in a direction toward the manuscript. Therefore, it is difficult to bring the protrusion 70c of the frame and the transparent plate 60b into close contact along an entire length of an image sensor extending in a vertically going away direction on FIG. 8, whereby gaps are partially formed between the frame 70 and the transparent plate 60b. 
The conventional contact-type image sensor is constructed as described above, wherein there are problems that a conveying mechanism is difficult to design because it is necessary to bend the conveying passage of the manuscript when the protrusion of the frame does not have a height same as that of the surface of the transparent plate, on which the manuscript is conveyed, whereby the manuscript is easily jammed.
Further, when the height of the protrusion of the frame is same as the height of the surface of the transparent plate, on which the manuscript is conveyed, it becomes difficult to bring the contact portion between the frame and the transparent plate into close contact along the entire length of the image sensor because of dimensional tolerances of various contact surfaces between the protrusion and the transparent plate, the warp of the transparent plate in a longitudinal direction, and so on, whereby gaps are partially formed between the frame and the transparent plate. Therefore, when dust intrudes from the gaps by vibration of the roller at time of conveying the manuscript, or the surface of the plate is cleaned by a solvent, such as alcohol, to remove dirt of the transparent plate, an extraneous matters intrude into an inside along with the solvent from the gaps, whereby there are problems that the extraneous matters interrupt a path of light and the light-and-shade information of the image of the manuscript is not correctly transferred to the sensor ICs.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide a contact-type image sensor, which can prevent a manuscript from jamming dust, a solvent and extraneous matters from intruding into the image sensor even though there is dimensional tolerances, a warp of a plate, or the like, and correctly transmits light-and-shadow information of an image of the manuscript to a sensor IC.
According to a first aspect of the present invention, there is provided a contact-type image sensor comprising: a plate positioned in a manuscript guiding path, which plate has at least a transparent portion; a light source illuminating a manuscript through the transparent portion of the plate; a frame holding the plate; and a lens receiving a light reflected by the manuscript and forming an image in a sensor IC, wherein a recess formed in the frame is engaged with a protrusion formed in the plate, and the heights of surfaces of the frame and the plate on sides of guiding the manuscript are substantially the same.
According to a second aspect of the present invention, there is provided the contact-type image sensor, wherein the protrusion of the plate is formed such that at least two plates or more are attached to both ends of the plate, positioned on a manuscript guiding surface, so as to protrude from the both ends.
According to a third aspect of the present invention, there is provided the contact-type image sensor, wherein the protrusion of the plate is formed such that two plates having different widths are overlapped and attached to the plate so that steps engaging with the recess are formed on both sides of the plate.
According to a fourth aspect of the present invention, there is provided a contact-type image sensor comprising: a plate positioned in a manuscript guiding path, which plate has at least a transparent portion; a light source illuminating the manuscript through the transparent portion of the plate; a frame holding the plate; and a lens receiving a light reflected by the manuscript to form an image in a sensor Ic, wherein a recess formed in the frame and a protrusion formed in the plate are engaged, a surface of the frame on a side of inserting the manuscript is higher than the plate, and a surface of the frame on a side of ejecting the manuscript is lower than the plate.